If you're late for lunch and you're Marla Gibbs, don't apologize. Just crinkle your eyes like a bashful sphinx and spin a quick tale about helping the chauffeur change a wheel, the way Mary Jenkins of "227" would.

Hal Williams, Gibbs' husband in the NBC sitcom, has been holding the fort during the wait, poking gentle fun at his fictional spouse. "Leaving Marla to shop in a boutique is a dangerous thing," he says with the knowing tone of a real husband.

"Oh, you heard about the boutique, huh?" mutters Gibbs to an associate, as she sits down to eat.

Gibbs and Williams, here over the weekend with a bevy of producers and support personnel, are having a blast. Riding high on a new contract for another season's worth of "227," they have come to Washington on something between a good-will visit and a researchers' field trip. The idea is to find out more about the city where their characters live and to get ideas for new episodes.

"We want to keep making references to things in Washington in the show," Williams says, "to eliminate doubt about where we are."

In fact, the only genuine piece of Washington in "227" -- the show is taped in Los Angeles -- is a quick overhead shot or two of the city in the title sequence. And although one of Gibbs' daughters went to Howard University and a Williams daughter graduates from Georgetown University law school this week, there isn't a whole lot of D.C. in either of these two visitors.

"I'm from Chicago," Gibbs declares.

"Columbus, Ohio," says Williams.

At any rate, husband and wife (Mr. and Mrs. Lester Jenkins of 227 Somewhere-in-D.C. Rd. NW) are having lunch at the Madison, although chances are the Jenkinses would never eat at a fancy place like this. And this happily married twosome (both are divorced in real life) are clearly enjoying their TV marriage. To watch them interact at the table is to see a couple who have apparently shared children and good-naturedly thrown plates at each other for years.

"When are you going to admit you can't see the menu?" asks Williams after Gibbs has squinted at the chef's suggestions for several minutes.

"I was waiting for you to help me," says Gibbs with mock meekness.

Williams, a large, rugged man who looks as if he should be spiking footballs instead of acting in his fifth TV series, pulls the menu away from his wife with a martyr's exasperation. He orders Gibbs blackened redfish, clam chowder and tonic water before she can open her mouth. Gibbs (or is it Mary Jenkins?) sighs with gratitude.

"This goes on all the time," says Williams. "We're in continuous rehearsal."

Mrs. Jenkins dissolves, and Marla Gibbs takes over. The maid who could dress down George Jefferson with a flick of the tongue in "The Jeffersons" has moved up in the world. Now she's not only the star of a new show, she's a producer. And she's talking now about a product called Mary Jenkins.

"We're trying to make her different things, not just one thing, which I think is boring. At first we were trying to make her a sort of 'I Love Lucy' character, always getting into a lot of problems. But now Mary doesn't get into a lot of problems herself, she deals with other people's problems . . .

"We wanted the same ingredients as there were in 'The Jeffersons' -- we have old people, young people, a person working for tips, the up-and-coming couple -- the Jeffersons worked their way up. Lester's [Williams' character] worked his way up. Me, I'm a housewife . . . We have enough ingredients to address ourselves to different segments of the population. So everyone has a vested interest in watching the show."

This is no I-Am-Woman show. The idea, says Gibbs, is traditional family fare, in which Mother runs the home and brings up the children and Father (in this case a construction engineer) works all day. More practically, you need Mary Jenkins around in the daytime -- sitting on her milk crate on the stoop of 227 and cracking her brand of busybody, sometimes acidic jokes with her neighbors.

"I heard the O'Brians got a crack in their living room wall," a neighbor tells Mary Jenkins in the show. Mary shifts her milk crate closer to her friend.

"I heard the O'Brians got a crack in their marriage," she says conspiratorially.

"But they just celebrated their silver anniversary," protests the friend, spiking up another comic ball for Gibbs to slam down across the net.

"I can tell you one thing," she says. "They ain't going for the gold."

As a mother, Mary Jenkins has her children on a tight leash. "You being awfully nice, young lady," she says to her daughter, who is obviously trying to curry favor with Mom. "Now just what is it you going to ask me that I'm not going to like that you going to die if I don't do?"

The show has apparently struck a familiar chord, Gibbs says. "People say to me, 'You're just like my mother,' or 'You're just like my aunt.' I'm someone they know, and to me that means I'm real."

On this sunny Saturday morning, Gibbs, Williams and their "227" associates take a meander through Adams-Morgan. They have met with senior citizens, students, members of the press and District politicians. They've talked about Adams-Morgan's Ward 1, the District's August doldrums, the statehood debate. They've seen Logan Circle, they've even signed up to participate in Hands Across America by the White House. And now it's time to meet the people.

There aren't too many about the streets, but there are some smiling faces of recognition. There are a few unexpected reactions: A passer-by, an older woman in a worn coat, stops Gibbs and talks with her for a few minutes.

"I said I would like to be her maid," the woman says, "but she said she does her own work. Do you know how I could get in touch with Elizabeth Taylor?"

"Wow!" exclaims a restaurant manager, as the group enters his 18th Street establishment. "I gotta get an autograph. Oh, you all are my favorite. Oh wow, I'm shaking."

When they move on to an Ethiopian restaurant, the chef -- hampered by a language barrier -- does not understand what is going on. No number of polite smiles, laughs and waves can remove the look of fear on her face. They decide to leave in order to put her at ease.

"No time for no television," says Gibbs to the group as they walk out.

Accompanied by Councilman Frank Smith, who has brought along two aides sporting "Re-elect Frank Smith" buttons -- the three stop every available passer-by to extend greetings -- the group crosses the intersection of Columbia Road and 18th Street, the spiritual center of Adams-Morgan. The crowds are still light and the peals of recognition sparse. But when they reach Ontario Place, Mr. and Mrs. Jenkins have come home. A group on the porch of a house squeals out a welcome that has people coming out of every home.

" '227?' " says the first squealer. "It sure is. Oh my God. The two of them together. Oh, Ma! Oh my God." Five women alternately scream and hide their faces.

"Hey, it's Florence of 'The Jeffersons'!" shouts one. "Oh my God, I don't believe this."

Gibbs and Williams sign autographs for a long line of people: children, older women, young men. There is Sherron, and Irma (an old woman who pulls her autograph from her daughter's hands and tells her to get her own), Alice, Eric and Juju, Carol, Anne and Lee.

When the limos come to take the group away, it is proof to everyone that it really was Marla Gibbs and Hal Williams. Ontario Place waves goodbye. You'd think the pope and Princess Di had come through.

"People getting excited," says one limo driver as they pull away. "That's good."